feat(daemon): recognise our detached node, tail POSIX debug.log, more RPC threads

S12 - our node across sessions:
- The node the wallet launches is recorded in <datadir>/obsidiandragon-
  dragonxd.pid (pid + process start time + exe). A later session that
  finds it still running (after "Leave running" / keep_daemon_running)
  stops it gracefully on quit and waits for that exact process (no time
  limit, "Leave running" offered); never signals or kills it. A reused
  pid or a reboot never matches; stale records are deleted.
- stop_external_daemon is now honoured when this session only connected
  (no controller); it was ignored.

S13 - the node's own log on every platform:
- No -printtoconsole on Linux/macOS: the node writes its timestamped
  debug.log (which outlives the GUI) and we tail it next to the stderr
  pipe. Tail path from the datadir or the isolated override (Windows had
  %APPDATA% hard-coded, wrong for migrate-to-seed starts).
- After the node shrinks debug.log at startup, resume at this run's
  banner instead of re-reading the old run's tail.
- A node we didn't launch (left running, or found running) feeds the
  busy tracker from its debug.log, tied to the live process (our record,
  or POSIX hushd.pid) and only from lines it wrote. A GUI attaching to a
  node mid-rebuild now says "Node busy: rebuilding note witnesses" and
  asks before stopping it.
- A start that only finds a running node no longer resets the tracker;
  a found busy node shows the busy overlay at once.

S14: launch our node with -rpcthreads=16 unless DRAGONX.conf sets it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app_network.cpp

@@ -660,7 +660,11 @@ void App::tryConnect()
                             if (startEmbeddedDaemon()) {
                                 VERBOSE_LOGF("[connect #%d] Embedded daemon starting, will retry connection...\n", attempt);
                             } else if (daemon_controller_ && daemon_controller_->externalDaemonDetected()) {
-                                connection_status_ = TR("sb_connecting_generic");
+                                // A node already running (left running, or started by hand). If our probe reached
+                                // it but got no answer, say what it is doing (its log may show a rebuild) rather
+                                // than a bare "Connecting…" until the next attempt, up to 30s away.
+                                if (rpc::rpcKindMeansBusy(connectKind)) applyDaemonInitStatus(/*reachableButBusy=*/true);
+                                else connection_status_ = TR("sb_connecting_generic");
                                 VERBOSE_LOGF("[connect #%d] External daemon detected, will connect via RPC...\n", attempt);
                             } else {
                                 VERBOSE_LOGF("[connect #%d] Failed to start embedded daemon — lastError: %s\n",